1. Field of the Invention
The present invention relates to miniaturized viscometers and in particular to miniaturized viscometers capable of measuring the viscosity of nanoliter sized liquid samples.
2. Background Art
Measuring the viscosity of chemical and biological fluids is an important analytical tool in applications ranging from medical diagnostics and research to the chemical and manufacturing industry. In the paints industry, viscosity measurements aid in characterizing the fabrication and thickness of paints, varnishes, and coatings. Similarly, characterizing the viscosity of inks helps in ensuring uniform print and avoidance of smearing in both offset and ink-jet printing. In polymer rheology, intrinsic viscosity is widely used to measure the molecular weight of polymers, and the viscosity of melts and solutions is essential in designing processes such as injection molding and extrusion. The viscosity of biological solvents helps in gaining insight into the kinetics and dynamics of molecular and cellular processes such as conformational changes in protein. In addition, the viscosity of body fluids such as blood, blood plasma, amniotic, and synovial fluid plays an important role in diagnostic, prognostic, and preventive medicine.
Two commonly used viscometers are the cone and plate viscometer and the capillary viscometer. In the cone and plate viscometer, liquid is sheared between an inverted rotating cone and a stationary flat plate and the torque required to turn the cone at a known angular velocity determines the viscosity. While comparatively expensive, the cone and plate viscometer allows analysis of all aspects of rheological behavior. In capillary viscometers, liquid is made to flow through a capillary tube under a known pressure difference and the measured rate of flow is used to calculate the viscosity. The capillary viscometer, though inexpensive and simple to use, is mostly limited to Newtonian liquids due to the fact that the velocity in the tube and, therefore, the shear rate is constant.
Most current viscometers are designed predominantly as benchtop instruments that are difficult to use at the point of sample collection. Recently, a few miniaturized viscometers that measure viscosity using low sample volume have been developed.
Accordingly, there exists a need for a viscometer that is inexpensive and that uses low sample volumes that are, in particular, suitable for biological and medical applications.